1. Field of the Invention
The present invention relates to an endoscope system, processing apparatus for the same, and image generating method in which body function information such as an oxygen saturation level is visualized.
2. Description Related to the Prior Art
Recently in the medicine, an endoscope system including an illuminator, endoscope apparatus and processing apparatus has been used widely. In an endoscopic diagnosis with the endoscope system, normal light imaging is carried out by use of white light or broad band light as illuminating light. Also, special light imaging is carried out by use of narrow band light of which a range of a wavelength is made narrow as disclosed in JP-B 2648494.
In JP-B 2648494, information related to an oxygen saturation level of hemoglobin in blood from an image signal obtained by imaging a subject body is acquired by use of light absorption characteristic of blood vessels or scattering characteristic of body tissue. The information is visualized in a pseudo color image, to form an oxygen saturation level image. Thus, discovery of a cancer of which the oxygen saturation level is characteristically low can be facilitated by use of the oxygen saturation level image for diagnosis. Performance in the diagnosis can be higher.
According to JP-B 2648494, image information of two wavelengths are acquired, including a first wavelength component of which an absorption coefficient of oxyhemoglobin is larger than the absorption coefficient of deoxyhemoglobin, and a second wavelength component of which the absorption coefficient of the deoxyhemoglobin is larger than the absorption coefficient of the oxyhemoglobin. A relationship of largeness and smallness of the absorption coefficient of the oxyhemoglobin and the absorption coefficient of the deoxyhemoglobin is different between the first and second wavelength components. Thus, a difference in a pixel value between the value of the image information of the two wavelengths is changed largely by a change in the oxygen saturation level. A change in the difference in the pixel value is indicated as a color difference on the oxygen saturation level image. It is possible to understand an oxygen condition of blood vessels according to the color difference.
Also, in JP-B 2648494, third image information having components of an equal absorption wavelength range where the absorption coefficient of the oxyhemoglobin is equal to the absorption coefficient of the deoxyhemoglobin is acquired for comparing the pixel value of first image information including a first wavelength component and second image information including a second wavelength component. Accordingly, the image information of three frames is acquired for the purpose of forming the oxygen saturation level image of one frame in JP-B 2648494. It is likely that a frame rate is lower and followability of a motion image may be dropped upon occurrence of movement with a subject body.